Electric control system



Aug. 8, 1933. c. G. SUITS 1,921,788

ELECTRIC CONTROL SYSTEM Filed June 15, 1951 Fig.4.

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His Attorney.

UNITED STATES PATENT OFFICE ELECTRIC CONTROL SYSTEM Chauncey G. Suits, Schenectady, N. Y., assignor to General Electric Company, a Corporation of New York Application June 15, 1931. Serial No. 544,311

19 Claims. (Cl. 171--97) My invention relates to electric control sys characteristic of circuit 1, it will be seen that in tems and particularly to selective control systems, the region a the current is small, this region corwherein the control is efiected by variations in responding to the unsaturated condition of the the voltage of an alternating current circuit. iron core of the inductor 2; the current is large One object of my invention is to provide an imin the region 0, which region corresponds to a 60 proved control system in which an electro-recondition of saturation of the iron core and in sponsive device may be caused to operate in a the region b occurs the most rapid change in curpredetermined manner in response to voltage rent with voltage changes which is the most sigvariations of an alternating current circuit. Annificant characteristic condition for this circuit.

other object of my invention is the provision of In this region b it is found that in response to a 5 an improved control system in which a plurality very small change in applied voltage the current of electro-responsive devices may be selectively rises to such a maximum value that the capacioperated in accordance with the voltage of an tance and inductance voltages become equal in alternating current circuit. magnitude for a portion of the cycle, resulting My invention will be better understood from in a quasi-resonance state called non-linear reso- 7 the following description taken in connection nance. I have found that the critical voltage 'for with the accompanying drawing, and its scope non-linear resonance or simply the resonant will be pointed out in the appended claims. voltage does not depend upon the capacitance Referring to the drawing, Fig. l is a diagram or the resistance in the circuit critically, while of a simple series non-linear circuit; Fig. 2 shows the variation of the voltage with frequency is ap- 75 a. typical volt-ampere characteristic of the cirproximately linear. The most significant single cuit shown in Fig. 1; Fig. 3 is a diagram of a factor in determining the resonant voltage is the non-linear bridge circuit illustrating one form nature of the saturation characteristic for the of my invention; Fig. 4 shows two voltage curves iron of the reactor core. For a given material,

obtained with a bridge circuit such as shown in however, the critical voltage varies approximately 0 Fig. 3; Fig. 5 is a circuit diagram illustrating anas the number of turns on the core. other form of my invention; Fig. 6 is a chart In Fig. 3, I have shown two series non-linear illustrating the operation of the system shown in circuits of the type illustrated by Fig. 1 combined Fig. 5; Fig. '7 shows a family of volt-ampere charto produce a bridge circuit having the two acteristics illustrating the'hysteresis phenomenon branches designated by A and B. Each of these in a series non-linear circuit; Fig. 8 shows a branches comprises an inductor, a resistor and modification of what is shown in Fig. 5; Fig. 9 is a a capacitor corresponding to the respective elechart illustrating the operation of the system ments of the circuit shown in Fig. 1 but with this shown in Fig. 8; and Figs. 10 and 11 show nondifference, that the inductors of the two branches 35 linear bridge circuits which are independent of A and B differ slightly in the number of turns. frequency variations. Circuit connections 5, 6, are shown connected to Primarily my invention is dependent upon the the respective branches A and B between the caoperation of a circuit comprising elements of capacitor and resistor elements. Were the two pacitance and resistance in conjunction with elebranches A and B to comprise identical elements 40 ments of inductance of such nature that the magthe voltage 2 between the connections 5 and 6 nitude of the inductance depends upon the cur would remain theoretically Zero for all values of rent therein. Inductive characteristics of this applied voltage D. By making the inductance of nature are obtained for example for coils in one branch, however, different from that of the which closed cores of ferro-magnetic material other branch even by a very small percentage the 45 are employed. Circuits of this description are two branches of the bridge can be made to beusually distinguished by their non-linear voltcome resonant at values of applied voltage which ampere characteristics and are termed therefore differ from each other by a small amount. This non-linear circuits. To assist in the clear undereffect is represented in Fig. 4 where the voltage standing of my invention I will first refer to curve 7 shows that up to an applied voltage of 50 Fig. 1 which shows a series non-linear circuit 1 approximately 109 volts neither circuit is in a comprising the saturable core inductor 2, the recondition of non-linear resonance; hence, the sistor 3 and the capacitor 4 connected to the voltage e is of negligible value. When the apsource V of a constant frequency variable voltplied voltage reaches a value of 109 volts, howage alternating current. ever, one of the two branches attains its critical 55 In Fig. 2 where I have shown the volt-ampere voltage and the current therein rises rapidly 110 V producing a high voltage e between the condensers. This voltage is maintained until the applied voltage becomes equal approximately to 111 volts at which point the critical voltage is reached for the other branch of the circuit. As soon as both circuits are in non-linear resonance the voltage e again assumes a low value which is maintained for all subsequent increases in the applied voltage. If now the applied voltage is decreased from a high value the characteristic 7 may be retraced exactly. Since the resonance voltage depends predominately upon the number of turns on the inductor this voltage may be made to asume any convenient value within wide limits; thus the extent of the voltage selective region for a given bridge circuit may be easily determined and is in fact equal to the difierence in the resonant voltages for the two branches of the bridge. The curve 7 shown in Fig. 4 may for example be obtained if the bridge circuit shown in Fig. 3 employs inductors 2 and 2 having respectively 480 turns and 490 turns on cores of identi cal material, size and shape, resistors having 60 ohms each and capacitors having 28 mi each. At 8, I have shown the voltage curve obtained with the same circuit in which the resistor and capacitor values of the two branches are the same as before but the inductor values respectively are 480 turns and 568 turns.

The performance of this bridge circuit thus far described is had for constant frequency and changing voltage. It will be obvious from the dependence of the resonant voltage upon frequency that the region of voltage for which the condenser difference voltage 6 is large, may be changed by altering the frequency of the supply source, thus providing a second means of control.

Having thus briefly described the fundamental characteristics of a non-linear bridge circuit I will describe the various modified forms of my invention which I have chosen to illustrate in this application. In Fig. 5, I have illustrated a selective control system employing a series non-linear bridge circuit by which a number of load circuits may be controlled selectively in response to variations in the voltage applied to the system. The bridge circuit 10 is shown having four series non linear branches designated C, D, E, and F and as being connected through the potentiometer 11 with the variable voltage alternating current source V. As in Fig. 3, the several branches are identical with the exception that each diflers from the other in the inductance of the inductor member, the diiference in inductance being indicated on the drawing by a difierence in the number of turns in the inductor windings. By connections between each branch circuit and each other branch circuit I am able to control selectively the several load circuits 12 to 17 inclusive shown connected to a common source of power 18, such as an alternating current circuit, and each including a load device 19, the control of each circuit being effected through a suitable relay or electro-responsive device 20 such for example as a, vapor electric discharge device.

The operation of the various load circuits in response to a resonance condition in each of the several branches of the bridge circuit 10 is represented by the chart comprising Fig. 6 wherein the several hatched portions 22 represent the response of the several load circuits 12 to 17 inclusive. In this figure the critical voltages of the several branches C, D, E, and F are represented by the vertical lines Vc, VD, VE and VF respectively. Thus .as the applied voltage V is steadily increased, load circuit 12 is operated between limits V0, V1); load circuit 14 is operated between limits VE, VF; load circuit 15 is operated between limits Vc, VE, etc. from which it will be seen that each of the several load circuits is operated for a definite voltage range only which is different from that of each of the other load circuits.

While I have chosen to show in Fig. 5 a bridge circuit having four branches it is to be understood that my invention is not limited to a circuit having any particular number of branches. In its simplest form the circuit may have but two branches such as is shown in Fig. 3 in which case a single electro-responsive device affected by the voltage e may control a single load circuit.

In Fig. '7, I have shown a family of volt-ampere characteristics for various values of resistance in a series non-linear circuit such as shown in Fig. 1. In this figure curves 1, g, h, z, and 7' show the characteristics taken of a series non-linear circuit of which the inductance for all curves was 484 turns on a closed core of silicon transformer steel, and the capacitance was 14 microfarads. The resistance in the circuit for the respective curves was 40, 60, 82, 99 and 124 ohms. From Fig. '7 it will be observed that for values of resistance less than a certain critical value the curve for increasing voltage does not coincide with the curve for decreasing voltage. The value of the increasing voltage for which the current rises rapidly has been called the critical voltage for non-linear resonance or simply the resonant voltage; similarly the value of decreasing voltage for which the current suddenly drops to a low value will be referred to as the critical voltage for dissonance in non-linear circuits or simply the dissonant voltage. It will be observed from Fig. 7 that the dissonant voltage may easily be varied by changing the resistance in the circuit and that this may be done without materially changing the resonant voltage; hence the resonant voltage of a branch and accordingly the operating or pick-up voltage of the electro-responsive device connected therewith is determined by inductance alone while the dissonant voltage of the branch or the deenergizing voltage of the electro-responsive device is adjustable by a variation of the resistance almost to the exclusion of other factors. I desire to emphasize that in order to obtain the volt-ampere characteristic shown in Fig. 2 the variation in voltage should be smooth and continuous, such for example as that provided by an induction regulator. From the curve shown in Fig. 7 it becomes apparent that load circuits may be actuated in a diiTerent sequence for increasing voltage than that which obtains for decreasing voltage, thus making use of the double valued property of the series non-linear circuit.

In Fig. 8, I have shown the modified bridge circuit 25 having series non-linear branches G, H, and I in which I take advantage of this property. The several branches in this modification have capacitors of the same value but have inductors of different values and resistors of dilTerent values. The several branches are interconnected as in Fig. 5 to control load circuits 26, 2'7, and 28 each having a translating device 29 therein and connected to the common supply circuit 30, each load circuit being controlled by an electro-responsive device 31, such for example as a vapor electric discharge device.

The operation of the circuit 'shown by Fig. 8 is illustrated by the chart comprising Fig. 9. In this chart the hatched portions 33 represent the response of the load circuits 26, 2'7, and 28 to resonant voltages and hatched portions 34 represent the response of the same load circuits to dissonant voltages. In this figure the critical voltages for branches G, H, and I when the applied voltage is increased are represented by the vertical lines Va, VH, and V1 included in the bracket marked Res. while the critical voltages for these branches when the applied voltage is decreased are represented by the vertical lines VG, VH, and V1 included in the bracket marked Dis.

In considering the non-linear bridge circuits described above, it has been assumed that the applied voltage had constant frequency. If, however, the frequency of the applied voltage varies, the particular value of the applied voltage at which the bridge becomes responsive changes in such a manner that for restricted regions that value of the applied voltage is proportional to the frequency. This follows fundamentally from the change in resonant voltage for the series resistance, capacitance, saturating inductance circuit of which the bridge is formed. In most applications such frequency dependence is of little or no consequence; however, in certain cases it becomes desirable to remove this feature. In Fig. 10, I have shown how the effect of frequency variation may be overcome in a control circuit comprising a non-linear bridge circuit having two branches, the inductance, resistance and capacitance elements of which are numbered the same as the corresponding elements in Fig. 3. In the A. C. circuits supplying the two branches are the two capacitors 36 and 36' respectively and shunted about the two branches are the resistances 3'7 and 3'7 respectively. By this arrangement the voltage of the output circuit controlling the load circuit is rendered independent of frequency variations.

In Fig. 11, I have shown a modified circuit for eliminating the effect of frequency changes which circuit is adapted for use in a multiple bridge arrangement such as shown in Figs. 5 and 8. The essential features of this modified form are the same as in Fig. 10, the capacitor 38 being employed in the A. C. supply circuit and the resistance 39 being arranged in shunt to the several branches of the bridge circuit. The condenser, resistance circuit shown is but one of a number of circuits by means of which the dependence of the resonant voltage on frequency may be minimized or removed. An essential feature of all such frequency compensating circuits is the provision of a branch voltage which changes with frequency in the same degree and direction as the resonant voltage of the non-linear circuit which it supplies.

From the above disclosure it will be seen that I have provided a voltage controlled system whereby a plurality of load circuits may be selectively closed and opened independently of one another and each be maintained closed through a different predetermined range of the control voltage. By a modified form of my invention the selective closing and opening of the several load circuits may be effected for a plurality of different values of the control voltage whereby each load circuit may be maintained closed through a plurality of different predetermined ranges of the control voltage. I desire it to be understood that the drawing forming a part of my present application is merely a diagrammatic representation of my invention, the relative proportions of several inductors and resistors not being intended to be a measure of the actual values of those members. The spacing of the voltage verticals in the charts comprising Figs. 6 and 9 although shown more or less uniformly spaced may in practice be spaced in any desired irregular manner. I also desire it to be understood that by the expression means entirely electrical in operation employed in certain claims I refer to the non-linear circuits which function in a purely electrical manner and consist of parts all of which are fixed relatively each to the other. Thus this expression is intended to distinguish over electro-mechanical apparatus having mechanically moving parts such for example as electro-magnetic relays.

I have chosen the particular embodiments described above as illustrative of my invention and it will be apparent that various other modifications may be made without departing from the spirit and scope of my invention which'modifications I aim to cover by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A control system comprising an alternating current circuit having a variable voltage applied thereto, an electro-responsive device and resonant circuit means dependent upon the voltage of said circuit for rendering said device operative through a limited portion of the total range of voltage variation the limits of said portion being intermediate the limits of said range.

2. A control system comprising an alternating current circuit having a variable voltage applied thereto, an electro-responsive device and resonant circuit means responsive to successive changes of voltage in said circuit in the same cli-' rection for rendering said device operative and subsequently inoperative.

3. A control system comprising an alternating current circuit having a variable voltage applied thereto, an electro-responsive device and resonant circuit means responsive to a continuous change of said voltage in the same direction and independent of frequency for rendering said device operative and subsequently inoperative.

4. A control system comprising an alternating current circuit having a variable voltage applied thereto, an electro-responsive device and means comprising a plurality of non-linear circuit between the alternating current circuit and the device for rendering the device operative and subsequently inoperative in response to a change of said voltage in the same direction.

5. A control system comprising an alternating current circuit having a variable voltage applied thereto, a plurality of non-linear circuits connected with said circuit and constructed to have different resonant voltages and a relay having its control circuit connected between said nonlinear circuits.

6. A control system comprising an alternating current circuit having a variable voltage applied thereto, an electro-responsive device and means entirely electrical in operation and dependent upon the voltage of said circuit for rendering said device operative through a limited portion of the total range of increasing voltage and through a totally different portion of the total range of decreasing voltage.

7. A control system comprising an alternating current circuit having a variable voltage applied thereto, an electroresponsive device and means entirely electrical in operation and dependent upon the voltage of said circuit for rendering said device operative through a limited portion of the total range of increasing voltage and through a different limited portion of the total range of decreasing voltage, said portions being spaced from each other.

8. A selectivecontrol system comprising an alternating current circuit having a variable volt age applied thereto, a plurality of electro-responsive devices, and resonant circuit means responsive to the variations of said voltage for selectively operating any single device of said plurality of devices.

9. A selective control system comprising an alternating current circuit having a variable voltage applied thereto, a plurality of electro-responsive devices, and non-linear circuit means responsive to the variations of said voltage for selectively operating any one device independently of the remaining devices.

10. A selective control system comprising an alternating current circuit having a variable voltage applied thereto, a plurality of electro-re sponsive devices, and means consisting of parts fixed relatively to each other for supplying energy from said circuit to said devices for individually operating the devices selectively in response to said voltage variations. 11. A selective control system comprising an alternating current circuit having a variable voltagenapplied thereto, a plurality of electro-responsive devices, and means comprising a plurality of non-linear circuits controlled by the voltage of the circuit for causing each device independently of the others to be operative through a predetermined voltage range.

12. A selective control system comprising an alternating current circuit having a variable voltage applied thereto, a plurality of electro-responsive devices, and non-linear circuit means connecting said devices With said circuit for causing a predetermined operation of any device independently of theremaining devices under the control of said voltage.

13. A control system comprising an alternating current circuit having a variable voltage applied thereto, a plurality of non-linear circuits connected therewith and constructed to have different resonant and disson'ant voltages and an electro-responsive device connected to respond to the diflerence of currents in said non-linear circuits.

14. A control system comprising an alternating current circuit, means for varying the voltage thereof, a plurality of similar non-linear circuits connected therewith and constructed to have different resonant and dissonant voltages. and a relay connected between corresponding portions of said non-linear circuits.

15. A selective control system comprising an alternating current circuit, means for varying the voltage of said circuit, a plurality of electro-responsive devices and means comprising a plurality of non-linear circuits responsive to the variations of said voltage for causing each of said devices to be operated over a different predetermined range of said voltage independently of the other devices.

16. A selective control system comprising an alternating current circuit, means for varying the voltage of said circuit, a plurality of electroresponsive devices and means comprising a plurality of non-linear resonant devices variably responsive to said voltage for controlling said devices in accordance with the variations of said voltage, each of said electro-responsive devices being connected to be responsive to the difference of the currents in two of said non-linear devices.

1'7. A selective control system comprising an alternating current circuit, means for varying the voltage of said circuit, a plurality of non-linear resonant circuits connected with said circuit and variably responsive to said voltage and a plurality of electro-responsive devices connected respectively between pairs of said circuits.

18. A selective control system comprising an alternating current circuit, means for varying the voltage of said circuit, a plurality of non-linear resonant circuits connected with said circuit and each responsive to a different circuit voltage and a plurality of relays connected respectively between various pairs of said circuits.

19. A selective control system comprising an alternating current circuit, means for varying the voltage of said circuit, a plurality of non-linear circuits connected with said circuit and constructed to have different resonant and dissonant voltages and a plurality of relays connected respectively between various pairs of said non-linear circuits.

CHAUNCEY G. SUITS. 

